The present disclosure relates generally to hydrogen storage, and more particularly to methods for enhancing hydrogen spillover and storage.
The U.S. Department of Energy (DOE) has established a multi-stage target for hydrogen storage capacity in materials, for example, those materials intended for fuel cell applications. The targets for on-board hydrogen storage materials are about 1.5 kW/kg (4.5 wt %) by 2007, about 2 kW/kg (6 wt %) by 2010, and about 3 kW/kg (9 wt %) by 2015.
In attempts to meet the DOE targets, nanostructured carbon materials (e.g. carbon nanotubes, graphite nanofibers, activated carbon, and graphite) have become of interest to researchers as potential hydrogen adsorbents. However, it has been shown that nanostructured carbons (in particular, carbon nanotubes) have slow uptake, irreversibly adsorbed species, and the presence of reduced transition metals.
Experimental evidence, combined with ab initio molecular orbital calculations of hydrogen atoms on graphite, has led to the proposal of a mechanism for hydrogen storage in carbon nanostructures involving hydrogen dissociation on metal particles followed by atomic hydrogen spillover and adsorption on the nanostructured carbon surface. Hydrogen spillover was first postulated in the early 1960s, and despite continued investigations and research to support the theory, the mechanistic details of hydrogen spillover are still poorly understood.
As such, it would be desirable to provide methods for enhancing hydrogen spillover and increasing hydrogen storage capacity.